Can not upgrade to a deal advertised on the Telkom website

I have a Wifi contract which is currently a sim only month to month contract. I currently get 10 gig day and 10 gig night data. I want to increase m data to the offer for 20 gig day and night time data sim only month to month contract. I logged 2 requests for an upgrade, phoned 10213 twice with no answer and sent an e-mail to 10213. I was finally called by a consultant but I was told that if I can not upgrade/change to the offer advertised on their website. I am trying to avoid cancelling my current month to month sim only deal and applying for a new deal for the 20 gig day and night data ,month to month sim only offer which would be a lengthy process and inefficient.